Oxidation-Sulfidation Behavior of Ni Aluminide in Oxygen-Sulfur Mixed-Gas Atmospheres.

摘要

As part of a development effort on nickel aluminides based on Ni sub 3 Al as structural materials for fossil energy applications, oxidation/sulfidation studies are being conducted at Argonne National Laboratory on materials that are being developed at Oak Ridge National Laboratory. Sheet samples of nickel aluminide, containing 23.5 at. % Al, 0.5 at. % Hf, and 0.2 at. % B were tested in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made by a thermogravimetric technique in exposure atmospheres of air, a low-p/sub O sub 2 / gas mixture, and low-p/sub O sub 2 / gas mixtures with several levels of sulfur. Detailed scanning electron microscopy, x-ray, and electron microprobe analyses of the corrosion product scale layers were conducted. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low-p/sub O sub 2 / environment developed an aluminum oxide scale. As the sulfur content of the gas mixture increased, the alumina scale exhibited spallation and the alloy tended to form nickel sulfide as the reaction phase. The results indicated that the sulfidation reaction of nickel aluminide specimens (both bare and preoxidized) was determined by the rate of transport of nickel from the substrate through the scale to the gas/alumina scale interface, the mechanical integrity of the oxide scale, and the H sub 2 S concentration in the exposure environment. 13 refs., 32 figs., 3 tabs. (ERA citation 12:031095)